This invention relates to a sprocket wheel for driving and/or guiding a drive chain for a scraper-chain conveyor or a mineral winning machine such as a coal plough. The invention is particularly concerned with a sprocket wheel for use with a drive chain having chain links made from rod of circular cross-section.
Sprocket wheels of this type have a plurality of equi-spaced circumferential teeth. The adjacent teeth define pockets for the reception of the links of a drive chain. Each of the teeth is of two-part construction, the sprocket wheel being formed with a central circumferential groove which passes through all the teeth thereby defining their two-part construction. Alternate links of the chain lie within the pockets as the chain passes round the sprocket wheel, and the remaining links (which lie substantially at right-angles to the first-mentioned links) are accommodated in the groove. The two ends of each pocket are defined by flanks formed on the mutually-facing portions of the two parts of each of the teeth defining that pocket. The tooth flanks at the two ends of each pocket converge slightly, and define chain link bearing faces. The flanks merge with rounded faces which define the bases of teeth.
When a sprocket wheel of this type is used to drive the drive chain of a scraper-chain conveyor or a mineral winning machine, the links of the drive chain are subjected to extremely high loads. Despite the use of drive chain having increasingly heavier cross-sections and considerably improved quality, it has hitherto not been possible to increase the service life of drive chains to any appreciable extent. The pattern of the breakdowns that have occurred in use have lead to the conclusion that a considerable proportion of the damage done to the chain links is attributable to unsatisfactory co-operation between the chain links and the sprocket wheel.
The teeth of known sprocket wheels are of symmetrical shape, the radii of the rounded faces at the bases of the teeth being approximately equal to one half of the thickness of each chain link. This form of sprocket wheel has the advantages of being unaffected by the unavoidable variations in the sizes of the chain links that occur during manufacture, and of precluding jamming of the chain links against the teeth (which could make it difficult to remove the links from the pockets at the chain-outlet side of the sprocket wheel). Unfortunately, this type of sprocket wheel has the disadvantage that the first tooth of the sprocket wheel usually has to take up the entire tensile force of the chain. This results in considerable stress being concentrated at this tooth.
In order to distribute the tensile force of the chain over several teeth, a sprocket wheel is known in which the radii of the rounded faces at the bases of the teeth are increased so that they are about 20-80% larger than half the thickness of the chain links. Unfortunately, a sprocket wheel of this type can only be used when the variations in the sizes of the chain links are relatively small. Moreover, even though its teeth are symmetrical, there exists the danger of jamming between the chain links and the teeth. This type of sprocket wheel is described in DE-AS 2856099.
The aim of the invention is to provide a sprocket wheel which does not suffer from these disadvantages.